The presently available space heating and domestic hot water heating systems have several serious limitations in their performance and reliability. The heat transfer mechanism is inefficient and unreliable. The typical forced-liquid system requires a circulation pump which consumes electricity. The temperature differential between the collector and the water truck is quite large , e.g., 30.degree. F. The coolant is usually corrosive and subject to freezing. Many coolants are highly toxic (hence hazardous) should there be incursion to the hot water system. The controls are complicated and may not prevent transfer of heat from the condenser to the collector. The typical installation is neither optimum nor reliable.
The thermal advantage of a phase-change system over a circulating-liquid system is apparent from corsideration of latent heat as opposed to sensible heat for energy transport. The heat absorbed using a circulating liquid is expressed by EQU q=mC.sub.P (T.sub.out -T.sub.in)
where m is the flow rate of circulating liquid, C.sub.P is the specific heat of the liquid, and T.sub.out and T.sub.in are the temperatures of the liquid leaving and entering the collector.
The comparable expression for the phase-change system in which liquid enters the collector, boils with no change in temperature, and leaves as a vapor, is EQU q=m (h.sub.g -h.sub.f)
where h.sub.g and h.sub.f are enthalpies of the vapor and liquid respectively, with their difference being the latent heat of vaporization.
The latent heat of a common refrigerant, Freon 114, is over 40 BTU/lb., compared to the specific heat of water of 1.0 BTU/lb-.degree.F. This means that the circulating rate of the fluid for the phase-change system can be a small fraction of that of a circulating liquid, along with comparable elimination of external pumping power. Reduction of the circulating rate in the circulating liquid system would produce higher collector temperatures, accompanied by higher collector losses.
The standard pumped coolant system can neither maintain isothermal conditions within the collector nor provide the automatic maximum heat transfer in the transiently-cooled section of the tank when cold water enters caused by the increased condensing action at that point. Furthermore, the increase in heat transfer, as described above, in connection with a phase-change system, comes only from the collector; no heat is robbed from the upper portion of the tank which was previously heated. Thus, a beneficial stratification in the water tank is preserved despite the presence of the condenser. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.
It is, therefore, an outstanding object of the invention to provide a completely self-regulating heat recovery and transfer system.
Another object of this invention is the provision of a heat collection and transfer system which cannot freeze up.
A further object of the present invention is the provision of a heat collection and transfer system with improved heat transfer capability by using the phase change of the heat transfer fluid.
It is another object of the instant invention to provide a heat collection and transfer system which has no moving parts.
A still further object of the invention is the provision of a heat collection and transfer system which is more reliable and easily maintained than the prior art.
It is a further object of the invention to provide a heat collection and transfer system for which no outside controls are needed.
It is a still further object of the present invention to provide a heat collection and transfer system which eliminates many expensive and troublesome components.
Another object of the invention is the provision of a heat collection and transfer system which cannot lose heat from the condenser through the heat collector.
Another object of the invention is the provision of a heat collection and transfer system using a heat transfer medium which is non-corrosive.
Another object of the invention is the provision of a heat collection and transfer system using a heat transfer medium which has very low toxicity.
Another object of the invention is the provision of a heat collection and transfer system having a collector which is self-balancing and isothermal.
Another object of the invention is the provision of a heat collection and transfer system in which the stratification of the fluid to which heat is transferred in the condenser is improved.
Another object of the invention is the provision of a heat transfer and collection system in which heat always flows directly to the coldest point, improving system efficiency.
Another object of the invention is the provision of a heat transfer and collection system which will provide greater heat transfer and provide higher temperatures with otherwise unchanged collector and condenser capacities from more standard designs.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of elements set forth in the claims appended hereto.
Another object of the invention is the maintenance of high efficiency, when the system is used as a solar heat collector, for example, even if the collector becomes partially shielded from the sun (such as caused by a tree or building) during part of the day.
Another object is the efficient operation of the system even if the installation requires some of the collector system to have difference orientations, i.e., as in the case of a solar heat collector, on both the east and west slopes of a roof.
Another object of this invention is to provide a good performance monitor for the system.
Another object of this invention is to provide an effective test for even very small leaks in the system.